This invention relates to a device for encoding a pattern or picture, such as at least one hand-printed letter or a drawing, by predictive encoding. A pattern encoding device according to this invention is well applicable to a transmitter of a facsimile transmission system.
It is general on encoding a pattern into an encoded signal together with a background of the picture to resort to predictive encoding wherein correlation between successive information pieces, such as picture elements sampled from the pattern and the background, is utilized in order to compress the bandwidth or the amount of the encoded signal to be transmitted from a transmitter to a receiver or receivers and thereby to make an effective use of a transmission channel as regards both frequency and time. On the other hand, it is already known to pre-process the pattern with a view to achieving a higher compression ratio and consequently a higher transmission speed.
Thinning is an advantageous pre-processing scheme when an original pattern consists of at least one original line having an original line width of from one to several picture elements. According to the thinning process, such an original pattern is thinned in the transmitter into a thinned pattern consisting of at least one thinned line, each having a thinned line width of substantially one picture element and being representative of a skelton or a medial line of each original line. The thinned pattern as called herein is not visible but is represented by a pre-processed signal, which is encoded into an encoded signal, such as a run-length code signal, for transmission to the receiver or receivers. In the receiver, a signal representative of the thinned pattern is recovered from the encoded signal. The thinned pattern thus recovered is thickened into a reproduced or reconstructed pattern that is similar to the original pattern to a certain extent of faithfulness.
Thinning, however, is not always advantageous. Not a few original or unthinned patterns have to be encoded directly without thinning when the patterns reproduced in at least one of the receivers should be as faithful to the original patterns as possible. It is therefore desirable that a pattern encoding device be capable of encoding a variety of patterns selectively with the thinning process utilized to attain a higher transmission speed and without using the thinning process to thereby insure reproduction with a best possible degree of faithfulness.
As will later be described in detail with reference to a few of several figures of the accompanying drawing, different prediction rules or algorithms are necessary in a device for carrying out predictive encoding selectively for a thinned and an unthinned pattern. A conventional device for encoding information by predictive encoding, however, is operable in accordance with only one prediction rule. It has therefore been impossible to achieve predictive encoding selectively for the thinned and the unthinned patterns.